1. Field of Endeavor
The present invention relates to a spectrometer and more particularly to an echelle grating multi-order imaging spectrometer.
2. State of Technology
U.S. Pat. No. 5,717,487 for a compact fast imaging spectrometer, issued Feb. 10, 1998 to Donald W. Davies, and assigned to TRW Inc., provides the state of technology information reproduce below. The disclosure of U.S. Pat. No. 5,717,487 for a compact fast imaging spectrometer, issued Feb. 10, 1998 to Donald W. Davies, and assigned to TRW Inc. is incorporated herein in its entirety for all purposes.                “A spectrometer is a known instrument for examining the spectral characteristics of light. Light emitted from or reflected by an object is received within the spectrometer and separated into its spectral components, such as the red, green and blue colored spectra as occurs in equal intensity when standard white light is so analyzed. The intensity of each such spectral component of that received light may be readily observed and measured. Each element of nature, molecular components, organic and inorganic compounds, living plants, man, animal and other substances is known to emit a unique spectrum that may be used as an indicium to identify the emitter. In past scientific work, the spectral analyses of a host of known elements, molecules, materials, living plants, gases and the like, has been compiled into a library. That library enables objects and things to be identified solely by the spectrometric analysis of the light reflected therefrom. Thus, as example, by examining the spectral content of light reflected from the distant planets, astronomers identified the constituent elements, such as iron, forming those planets; by examining the spectral content of Gases emitted by factory smokestacks, scientists determine if pollutants are being emitted in violation of law or regulation; by examining the spectral content of land, the environmental engineer is able to determine the botanical fertility of a region and its mineral content, and, with subsequent observations, to determine the change in the environment with time; and by examining the spectral content of light reflected in multiple scans over a geographic region, military personnel identify camouflaged military equipment, separate from plant life, in that geographic region. The foregoing represent but a small number of the many known uses of this useful scientific tool.”        
U.S. Pat. No. 7,016,037 for an imaging spectrometer utilizing immersed gratings with accessible entrance slit, issued Mar. 21, 2006 to Michael P. Chrisp and Scott A. Lerner, provides the state of technology information reproduced below. The disclosure of U.S. Pat. No. 7,016,037 for an imaging spectrometer utilizing immersed gratings with accessible entrance slit, issued Mar. 21, 2006 to Michael P. Chrisp and Scott A. Lerner is incorporated herein in its entirety for all purposes.                “The present invention provides a compact imaging spectrometer. The spectrometer comprises an entrance slit, a catadioptric lens, a grating, and a detector array. The entrance slit directs light to the catadioptric lens; the mirrored surface in the lens receives the light and reflects the light back out of the lens to the grating. The grating receives the light from the lens and diffracts the light back to another portion of the lens. The lens then transmits and focuses the light onto the detector array. Small size for an imaging spectrometer is extremely important because it determines the requirements for the cryogenic cooling. For example, if the spectrometer is small it can fly in a small UAV. Also, if the spectrometer is small it is person portable. In one embodiment of the compact imaging spectrometer, the spectrometer has a front and a back. The entrance slit is located at or near the font and the detector is located at or near the back. The entrance slit, the mirror, the lens, the grating, and the detector array fit within an envelope located between the front and the back. In one embodiment the envelope is 71 mm long or smaller by 43 mm diameter or smaller.”        
U.S. Pat. No. 7,609,381 to David Wheeler Warren issued Oct. 27, 2009 for a compact, high-throughput spectrometer apparatus for hyperspectral remote sensing provides the state of technology information reproduce below. The disclosure of U.S. Pat. No. 7,609,381 to David Wheeler Warren issued Oct. 27, 2009 is incorporated herein in its entirety for all purposes.                Hyperspectral imaging is an extremely powerful and broadly applied technique of optical remote sensing. It consists of imaging an object or scene in a multitude of contiguous wavelength intervals. As distinct from multi-spectral imaging, where the wavelength intervals are typically defined by a relatively small number (e.g., <12) of discrete optical bandpass filters, hyperspectral imaging employs a larger number of finer spectral intervals in order to more reliably detect and discriminate between the unique spectral characteristics of natural and artificial materials.        As a tool of remote sensing, for example in geology or astronomy, hyperspectral imaging is generally practical only in wavelength regions where the earth's atmosphere is transparent over ranges of many kilometers and not affected by absorption from atmospheric constituents such as carbon dioxide and water vapor. These regions include the visible and near-infrared (VNIR: 0.4-1.0 μm), short-wave infrared (SWIR: 1.0-2.5 μm), mid-wave infrared (MWIR: 3.0-5.0 μm), and long-wave infrared (LWIR: 8.0-14.0 μm). Depending on the mission and phenomenology of interest, it is common to divide one of these broad spectral regions into 10 s or 100 s of sampled spectral sub-intervals. Typical numbers range from 32 to 512. These modest spectral resolutions are most practically achieved with spectrometers based on dispersive prism or diffraction grating elements.        In addition to large numerical aperture, spectrometers for hyperspectral remote sensing must have good image quality relative to the size of the detector element. For reliable processing and interpretation of the hyperspectral data, they should also have low image distortions such that the length of the slit image should not change with wavelength (keystone) and the dispersed position of the slit image for a given wavelength should not change with position along the slit (smile). These distortions should be controlled to a small fraction (e.g., < 1/10) of a pixel dimension.        Finally, spectrometers intended for aircraft or satellite use, where volume and mass are often highly constrained, must be as compact as possible. This is particularly true of instruments operating at infrared wavelengths, where the entire instrument is cooled to cryogenic temperatures and demands on cooling resources increase dramatically with instrument volume.        